The present invention is concerned with a communication control system and a communication control method and pertains in particular to a communication control system and a communication control method suitable for malfunction detection and malfunction detection function diagnosis of a plurality of input devices and output devices requiring high reliability and based on a central arithmetic processing unit.
The present invention can be utilized, as far as programmable electronic controllers used in plant control are concerned, as a means and a method to improve the safety of the devices at low cost, without making the devices complex.
With the technical advancement in the electronics and information technology fields, and the increased functional complexity and compositeness demanded of single devices becoming driving forces, the application range of programmable electronic devices is becoming wider and at the same time, the reliability demanded of programmable electronic controllers is becoming higher.
In the midst of scale increases and interlinking of plants advancing and highly automated plant operation also being carried out in recent years, there are also the problems of the spread of international safety standards and the lack of experienced and skillful staff, so on top of the safety measures built up since some time ago, a state is being reached in which further improvement in safety is required, and it has come to be regarded as important to prevent and mitigate, in their respective layers, the occurrence of accidents and the extension of damage.
In order to fulfill the aforementioned functional safety standards in plant controllers, it is required to operate surely in case an anomaly is detected, and in the unlikely event of there being a malfunction, it is demanded to stop the process on the safe side, so special design with serious consideration given to “safety” is required of a functional safety system. Technology of this kind of giving serious consideration to safety is e.g. described in JP-A-1994-290066.
In programmable electronic controllers, it is required to improve the hardware malfunction detection rate, so in order to satisfy this, it is common practice to load a variety of self-diagnostic functions. Moreover, there are required checks of whether these added self-diagnostic functions are actually operating, so policies such as embedding microprocessors in input devices and output devices implementing checks of the soundness of the self-diagnostic functions are carried out.